This invention relates generally to electrode compositions. In some specific embodiments, the invention relates to positive electrode compositions that can be incorporated into energy storage devices.
Metal halide batteries (for example, sodium-metal chloride batteries) including a molten metal negative electrode (usually referred to as the anode) and a beta-alumina solid electrolyte, are of considerable interest for energy storage applications. In addition to the anode, the batteries include a positive electrode (usually referred to as the cathode) that supplies/receives electrons during the charge/discharge of the battery. The solid electrolyte functions as the membrane or “separator” between the anode and the cathode.
When these metal halide batteries are employed in mobile applications, such as hybrid locomotives or plug-in electric vehicles (PHEV), the batteries may be subjected to a combination of charging and discharging rates. When discharging using high discharge current rates (for example, at 110 W), multiple discharge cycles may be conducted with no significant increase in resistance, increase in charging time, or loss of capacity. However, when discharging at low discharge currents, the metal halide (such, as sodium metal halide) batteries may degrade very rapidly, and the charging time may increase significantly.
Thus, there is a need for metal halide batteries having the desired performance attributes for applications involving slow discharge rates. Further, there is a need for improved positive electrode compositions to provide the desired performance attributes in the metal halide batteries.